The invention is related to a transmitter network comprising a source station for transmitting a signal via at least two transmission links to at least two transmitter stations, said transmitter stations comprising a receiver for receiving said signal from said source station and a radio transmitter for transmitting said signal on a carrier.
The invention is also related to a source station and a transmitter station for use in such a transmission network, and to a method of transmitting a signal.
A transmitter network according to the preamble is known from "DAB- A new sound broadcasting system, Status of the development, Routes to its introduction", by G. Plenge in EBU review technical, No. 246, April 1991,pp. 87-112.
When a conventional transmitter network is designed, for example, for broadcasting purposes, one is generally confronted with the problem that not enough channels are available for the signals to be transmitted. In that case one resorts to reusing frequencies and arranging the tramsmitters such that under normal propagation conditions it is possible to receive in a certain area only one of the transmitters transmitting at a specific frequency, so that no mutual interference need be expected under normal propagation conditions. In such a conventional transmitter network, however, interference may nevertheless occur under special propagation conditions, such as, for example, tropospheric ducting.
In the transmitter network known from the above mentioned article, a signal is transmitted with a like transmitter frequency via a plurality of transmitters, whereas a receiver can receive signals from different transmitters. As a result, a disturbance signal is developed having a characteristic corresponding to an echo signal. This (undesired) echo signal is suppressed in the receiver by means of an echo canceller or by using what is commonly referred to as a guard band in the time domain when the signal to be transmitted is actually transmitted. Consequently, it is possible that this received signal is discarded in the receiver for a specific period of time during which the received signal is disturbed by the echo signals.
A great advantage of transmitter networks, in which no more than a single transmitter frequency is used, is that much fewer channels need to be available than when conventional transmitter networks are used. In addition, in transmitter networks employing no more than a single transmitter frequency, there will be no additional disturbance even under special propagation conditions, because such disturbing signals are already taken into account in the receivers.
If the instant of transmission of a predetermined part of the signal differs too much between two transmitter stations, said echo delay can be rather long. This delay difference may be caused by delay differences of the transmission paths between the source station and the transmitter stations. As a result of these relatively large delay differences, the measures to be taken in the receivers for cancelling the effect of the echo signals are rather complex.
The signal to be transmitted by the transmit station can be in the form of a frame, comprising the useful data, a number of training sequences and/or sync symbols and sometimes stuffing symbols. The useful data can be supplied by the network consisting of transmission links. Such network often uses transport frame structures, in which the symbols to be transported have to be mapped. This mapping can be different for different transmission links. This may result in transmission of different symbols by the transmitter stations at a given instant, leading to a failure of the transmitter network.